We coninue to use the isolated rat liver perfused with a suspension of bovine red cells in Krebs-Ringer bicarbonate buffer, containing 3 per cent bovine serum albumin, as a model test system for evaluating the direct effects of hormones on the net biosynthesis of specific plasma proteins. The role of glucocorticoid in the induction of increased synthesis of acute phase proteins previously demonstrated for cortisol and corticosterone has been extended to dexamethasone; as little as 5 micron g percent of the latter elicits enhanced synthesis of fibrinogen, alpha 1-acid glycoprotein, alpha 2-(acute phase) globulin, and haptoglobin, while 0.5 micron g per cent is still effective for all but alpha 2-(acute phase) globulin. Isolation of free and bound polysomes and measurement of specific mRNAs for albumin and alpha 1-acid glycoprotein are being perfected to evaluate the role of changing levels of mRNA in the mechanism of action of glucocorticoid. BIBLIOGRAPHIC REFERENCES: Miller, L.L. Hormonal Regulation of Net Haptoglobin Biosynthesis in the Isolated Perfused Rat Liver. Plasma Protein Turnover, The Macmillan Press Ltd, New York, p. 441-451 (1976), ed. by R. Bianchi, G. Mariani, an A. S. McFarlane. Miller, L.L. The Definitive Role of Known Hormones in the Regulation of Net Biosynthsis of Five Acute Phase Plasma Proteins (APPP) by the Isolated Perfused Rat Liver: Corticosterone. Protides of the Biological Fluids, Vol. 23, Pergamon Press, New York, p. 461-469 (1976), ed. by H. Peeters.